Acid Base Concepts

Question 1

Equation for acid base homeostasis:

Answer 1

See image

Question 2

Henderson equation:

H+ =

Answer 2

24 x pCO2/ [HCO3-]

Question 3

Daily acid produciton =

pH ~ 7 = how many mmol?

How is acid/base homeostatis maintained?

Answer 3

~20,000 mmol acid

pH~7 = 140 nmol

buffering

Question 4

HCO3- is absorbed where and how?

Answer 4

in the Proximal tubule via carbonic anhydrase

Question 6

where is H+ excreated?

Answer 6

In the Collecting duct

Question 7

Components of arterial blood gas:

Components that make up basic chemistry:

Answer 7

pCO2 and pH

HCO3-, Na+, Cl-

Question 8

Your patient has Primary respiratory acidosis… What must his pCO2 be?

Answer 8

primary respiratoyr acidosis have pCO2 > 40mmHg

Question 9

Your pt has primary respiratory alkalosis… what does the pCO2 need to be?

Answer 9

pCO2 < 40mmHg

Question 10

Patient has primary metabolic acidosis, what must the HCO3- be?

Answer 10

HCO3- < 24mmol/L in primary metabolic acidosis

Question 11

Pt has primary metabolic alkalosis, what must our HCO3- value be?

Answer 11

HCO3- in primary metabolic alkalosis >24 mmol/L

Question 12

What two things could lead to acidosis?

Answer 12

Primary respiratory: CO2 > 40mmHg

Primary metabolic: HCO3-

Question 13

What two situations would cause alkalosis?

Answer 13

Primary respiratory: pCO2 < 40mmHg

Primary metabolic HCO3- >24 mmol/L

Question 14

Four steps for systematic approach to determine acid/base disturbances

Answer 14

1. pH (7.40 is normal)
2. Determine primary disorder

–metabolic or respiratory

3. Calculate expected compensation
4. Calculate anion gap

Question 15

What is meant by expected compenstation? Why is it important?

Answer 15

the body’s ability to appropriately compensate to primary acidosis or alkalosis.

If body cannot completely compensate, this is indicative of secondary disorder.

Question 16

What equation do we use for compensation in the case of metabolic acidosis (when HCO3- is <24 mmol/L)?

Answer 16

-pCO2 = 1.5 x [HCO3-] + 8

or

-pCO2 = last 2 digits of pH (only down to pH of 7.2)

Question 17

What equation do we use to calculate compensation for metabolic alkalosis (HCO3- >24 mmol/L)?

Question 18

pCO2 compensates in same direction as:

Answer 18

bicarb change

Question 19

Calculation used for Respiratory Acidosis (PaCO2 > 40)

Acute:

Chronic:

Answer 19

Acute: bicarb increase 1 mmol/L per 10 mmHg increase of PaCO2

Chronic: bicarb increases 4 mmol/L per 10 mmHg PaCO2

Question 20

What are the calculations for compensation in respiratory Alkalosis (PaCO2 <40 mmHg)

Acute:

Chronic

Answer 20

– Acute: bicarb DEcreases 2 mmol/L per 10mmHg PaCO2
– Chronic: bicarb DEcreases 4 mmol/L per 10 mmHg PaCO2

Question 21

If your patient has a pCO2 = 60 mmHg and is acidotic, what is our primary disorder?

What is the acute and chronic compensation of the bicarb (HCO3-)?

Answer 21

Respiratory acidosis

pCO2 = 60 mmHg (normal is 40 mmHg) thus increase of 20mmHg

HCO3- increase by 2 mmol/L (acute) and 8 mmol/L (chronic)

[Acute: bicarb increase 1 mmol/L per 10 mmHg PaCO2
– Chronic: bicarb increase 4 mmol/L per 10 mmHg PaCO2]

Question 22

Your patient is acidotic with a bicarb = 15 mmol/L

What is the primary disorder?

What will the expected compensation be?

Answer 22

Metabolic acidosis

pCO2 = (1.5 x 15) + 8 = 30 mmHg

Question 23

What cations and anions are taken into account when calculating the anion gap?

Answer 23

Na+ cation

HCO3- and Cl- = anions

Question 24

65 yo with history of ileus presented to surgical team.
NG placed to suction and next am had seizure.

pH = 7.63
pCO2 = 55
sO2 = 94 %

Na+ = 128 K+ = 2.9

Cl-= 70 HCO3- = 50

1. What is our primary disorder?

Answer 24

Patient is alkalemic, pCO2= 55 and HCO3- = 50

Primary metabolic alkalosis (HCO3- > 24mmol/L is alkalosis)

Question 25

65 yo with history of ileus presented to surgical team.
NG placed to suction and next am had seizure.

pH = 7.63
pCO2 = 55
sO2 = 94 %

Na+ = 128 K+ = 2.9

Cl-= 70 HCO3- = 50

Patient has primary metabolic alkalosis. What is the compensation?

Answer 25

with primary metabolic alkalosis, we compensate with pCO2-

Equation: –pCO2 = 0.9 x [HCO3] + 9

-pCO2 = 0.9 x [50] +9 = 54mmHg CO2

(our pts = 55mmHg CO2, thus is appropriately compensated)

Question 26

65 yo with history of ileus presented to surgical team.
NG placed to suction and next am had seizure.

pH = 7.63
pCO2 = 55
sO2 = 94 %

Na+ = 128 K+ = 2.9

Cl-= 70 HCO3- = 50

Calculate anion gap

Answer 26

[Na+] - [Cl- + HCO3-]

128 - [70 +50} = 8